Seattle Central CHEM 161 - Chapter02 - Atoms, Ions and molecules

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CHEM%1 61:%C hapter%2%N o te s%v0914% % page%1%of%10%CHAPTER 2: ATOMS, IONS, AND MOLECULES Problems: 2.1-2.78, 2.81-2.93, 2.94-2.96, 2.111-2.119, 2.121, 2.127 2.1 THE NUCLEAR MODEL OF ATOMIC STRUCTURE Joseph John (J. J.) Thomson (1897) carried out experiments with cathode rays. – His research group determined the charge-to-mass ratio of the particles in the rays. – They determined the particles were composed of tiny, negatively charged subatomic particles → electrons (e–) Eugen Goldstein (late 1880s) – Discovered canal (or anode) rays which were composed of positively charged subatomic particles → protons (p+) And decades later, James Chadwick won the Nobel Prize winner for his discovery (1935) → neutron (n) = neutral subatomic particle PLUM-PUDDING MODEL OF THE ATOM – Thomson proposed that the atom was a uniform sphere of positively charged matter in which electrons were embedded → electrons are like raisins in a pudding of protons THE NUCLEAR ATOM: PROTONS AND THE NUCLEUS – Ernest Rutherford was a scientist who did many pioneering experiments in radioactivity – He had members of his research group test Thomson’s Plum-Pudding Model using radioactive alpha (α) particles, basically helium atoms with a +2 charge and much bigger than an electron. Rutherford's Alpha-Scattering Experiment – Alpha (α) particles shot at a thin gold foil that’s only a few atoms thick – A circular detector is set up around the foil to determine what happens to the α particles. – If Plum-pudding Model was correct, the α particles should go through the foil like bullets through tissue paper. Experimental results: – Most of the α particles went straight through, but some were deflected or even bounced back!CHEM%1 61:%C hapter%2%N o te s%v0914% % page%2%of%10%Consider what the scientists expected to observe given each model. Rutherford’s interpretation of the results – Most alpha (α) particles pass through foil → Atom is mostly empty space with electrons moving around the space – Some α are deflected or bounce back →Atom must also contain a dense region, and particles hitting this region are deflected or bounce back towards source. → dense region = atomic nucleus (contains atom’s protons and neutrons) → Why this is called the NUCLEAR Model of the Atom Rutherford also estimated the size of the atom and its nucleus: Ex. 1: An atom is 100,000 times (105 or 5 orders of magnitude) bigger than its nucleus. If a nucleus = size of a small marble (~1 cm in diameter), indicate the length in meters then identify a common item that corresponds to that size for the following: a. 10 times bigger = ____________ m = __________________________ b. 100 times bigger = ____________ m = __________________________ c. 1000 times bigger = ____________ m = __________________________ d. 10,000 times bigger = ____________ m = __________________________ e. 100,000 times bigger = ____________ m = __________________________ nucleus (d~10-15 m)atom (diameter ~10-10 m)CHEM%1 61:%C hapter%2%N o te s%v0914% % page%3%of%10%Properties of Protons, Neutrons, and Electrons Subatomic Particle Charge Location Mass (amu) Proton +1 inside nucleus 1.00728 Neutron 0 inside nucleus 1.00866 Electron -1 outside nucleus 0.00055 2.2 ISOTOPES Each element always has the same number of protons, but the number of neutrons may vary. Atoms with different numbers of neutrons are called isotopes. – e.g. Carbon exists as carbon-12, carbon-13, and carbon-14 where each carbon atom has 6 protons but 6, 7, or 8 neutrons respectively – Isotopes are identified with an element name followed by the mass number – eg. uranium-235 (U-235), carbon-12 (C-12), cobalt-60 (Co-60), etc. Atomic Notation: – shorthand for keeping track of number of protons and neutrons in the nucleus atomic number (Z): whole number of p+ = number of e– in neutral atom mass number (A): whole number sum of protons and neutrons in an atom – Note electrons contribute almost no mass to an atom Complete the following table: Isotope Mass number # of protons # of neutrons # of electrons strontium-86 92Mo zinc-72 136Ba2+ 31P3− A review for section 2.3 Average Atomic Masses is available on the Chapter 2 Review from our class Website. E =element symbol Mass number= A Atomic number= ZCHEM%1 61:%C hapter%2%N o te s%v0914% % page%4%of%10%2.4 THE PERIODIC TABLE OF THE ELEMENTS METALS, NONMETALS, & SEMIMETALS Know which elements are metals, semimetals, nonmetals using the Periodic Table. Properties of Metals • shiny appearance • conduct heat & electricity • malleable: can be flattened into thin sheets • ductile: can be stretched into a wire • e.g. aluminum, copper, gold Properties of Nonmetals • dull appearance • brittle • nonconductor • e.g. carbon (graphite in pencils), sulfur Properties of Metalloids (or Semimetals): Have properties of metals and nonmetals – For example, silicon is shiny like a metal and acts as a semiconductor. %%%%%%%%%%%%%%%Copper%wires%% % % %%%%%%%%%%Sulfur%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%Silicon%CHEM%1 61:%C hapter%2%N o te s%v0914% % page%5%of%10%SOLIDS, LIQUIDS, AND GASES: KNOW the physical state of each element at 25°C! At standard state conditions (25°C and 1 atm): – Only mercury (Hg) and bromine (Br) are liquid – H, N, O, F, Cl, and all Noble gases (group VIIIA) are gases – All other elements are solids 2.5 TRENDS IN COMPOUND FORMATION chemical bond: what holds atoms or ions together in a compound COVALENT BOND and MOLECULES – 1st type of chemical bond: Covalent Bond – covalent bond: sharing of a pair of electrons by 2 nonmetal atoms – Two or more covalently bonded atoms form a molecule (or molecular compound) molecule: basic unit of a compound of covalently bonded atoms – Consider the HCl, H2O, NH3, and CH4 molecules below – Note how the chemical formula gives the actual number of each atom present in the following compounds:CHEM%1 61:%C hapter%2%N o te s%v0914% % page%6%of%10%Diatomic Molecules: – Recognize these elements that exist as diatomic molecules (X2): H2 N2 O2 F2 Cl2 Br2 I2 – Consider these the “diatomic seven” since there are seven of them,


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